I would have them ready when I went to bed, and turn it on if I got up to go to the bathroom or check on anyone in the early morning hours.
Seems my youngest is stirring around 3-4 am. I would not want them in for more than 12 hours just because it would make me nervous.
My Dh is a morning person. I would have him turn it on when he is up between 5 and 6 am.
You could put them in the micro for 5 mins to pre-heat then the crock if you wait till 8 am and 4+ hours on high.
I have made corn on the cob and baked potatoes together in the crock and they did great.